AWD Traction Torque Control Using Normalized Wheel Speeds
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Solution Overview
Problem
All-wheel drive vehicles face challenges in controlling torque during reduced or intermittent traction, as existing methods rely on non-driven wheels for speed estimation, which can lead to inaccurate wheel slip calculations and prolonged torque limitation even after traction is regained.
Innovation Solution
The method involves distributing torque to all wheels, computing normalized wheel speeds using measured rotational speeds, yaw rate, and wheel diameters, and adjusting the commanded torque level based on the difference between the fastest and slowest wheel speeds, with updates to wheel diameters and torque levels in response to changing conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If torque is limited to control wheel slip, then wheel slip is reduced, but vehicle propulsive force and productivity are reduced
Solution Approach 1:
The system dynamically adjusts the commanded torque level based on real-time wheel slip conditions. When wheel slip is detected, torque is limited to control slip; when slip ceases, torque is restored to driver demand levels, creating a dynamic response that resolves the contradiction between slip control and propulsive force
Solution Approach 2:
The system continuously monitors wheel speeds, calculates wheel slip, and uses this feedback to adjust torque levels. The controller calculates wheel slip by comparing measured wheel speeds against vehicle speed estimates, and adjusts commanded torque accordingly, creating a closed-loop control system that balances slip control with maintaining propulsive force
2Ease of operation
If wheel slip calculation relies on non-driven wheels, then vehicle speed can be estimated, but measurement precision deteriorates when non-driven wheels are slipping
Solution Approach 1:
The system uses all four wheels for both vehicle speed estimation and slip detection, rather than relying solely on non-driven wheels. By treating all wheels as potential sources of speed information and using the accelerometer as a supplementary measurement source, the system maintains measurement precision even when any individual wheel is slipping
Solution Approach 2:
The system introduces an accelerometer as an intermediary measurement device to estimate vehicle speed and longitudinal acceleration. This intermediary sensor provides an independent reference that does not depend on wheel rotation, allowing accurate wheel slip calculation even when all wheels are slipping
3Productivity
If torque is restored quickly after slip detection, then productivity improves, but wheel slip control reliability deteriorates
Solution Approach 1:
The system requires that wheel slip conditions cease for a predetermined time period before restoring full torque. This preliminary waiting period ensures that slip conditions are truly resolved before removing torque limitations, preventing premature torque restoration that would compromise slip control reliability
Solution Approach 2:
The system uses periodic monitoring of wheel speeds and continuous calculation of wheel slip to determine when torque restoration is appropriate. By periodically checking slip conditions and requiring a sustained period without slip, the system balances quick torque restoration with reliable slip control
Data Source
AI summary
A method of controlling torque in an all-wheel-drive vehicle limits the duration of loss of traction. During wheel slip events, a controller reduces the commanded torque from a driver demanded level. The controller calculates a normalized wheels speed for each wheel based on a measured yaw rate, measured wheel speeds, and calculated wheel diameters. The controller determines the end of the wheel slip event by comparing the normalized speeds of each while to one another.